    %     -----------------------------------------------------------------
    %
    %                              Ex6_15.m
    %
    %  this file demonstrates example 6-15.
    %
    %                          companion code for
    %             fundamentals of astrodynamics and applications
    %                                 2013
    %                            by david vallado
    %
    %     (h)               email davallado@gmail.com
    %     (w) 719-573-2600, email dvallado@agi.com
    %
    %     *****************************************************************
    %
    %  current :
    %            16 feb 19  david vallado
    %                         update for new constants
    %  changes :
    %            13 feb 07  david vallado
    %                         original baseline
    %
    %     *****************************************************************

    constastro;
    
    fprintf(1,'-------------------- problem ex 6-14 \n');
    ro = [0.0 0.0 0.0];
    vo = [-0.1 -0.04 -0.02];

    ralt = 590.0;
    dtsec = 0.0;

    [rint, vint] = hillsr( ro,vo, ralt,dtsec );

    fprintf(1,'initial interceptor position \n');
    fprintf(1,' r  %11.7f  %11.7f  %11.7f \n',rint);
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',vint);


    dtsec = 300.0;
    [rint, vint] = hillsr( ro,vo, ralt,dtsec );

    fprintf(1,' r  %11.7f  %11.7f  %11.7f \n',rint);
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',vint);

    dtsec = 1200.0;
    [rint, vint] = hillsr( ro,vo, ralt,dtsec );

    fprintf(1,' r  %11.7f  %11.7f  %11.7f \n',rint);
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',vint);


    dtsec = 600.0;
    [rint, vint] = hillsr( ro,vo, ralt,dtsec );


    fprintf(1,'-------------------- problem ex 6-15 \n');
    fprintf(1,'initial interceptor position \n');
    fprintf(1,' r  %11.7f  %11.7f  %11.7f \n',rint);
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',vint);

    dtsec = 300.0;
    [v] = hillsv( rint, ralt,dtsec );
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',v);

    dtsec = 900.0;
    [v] = hillsv( rint, ralt,dtsec );
    fprintf(1,' v  %11.7f  %11.7f  %11.7f \n\n',v);


